The present invention relates to a plasma display panel (hereinafter often referred to as "PDP") which is a plate display of a self-activation luminescence type using gas discharge, and more particularly to an electrode to be provided on a front or back plate of PDP.
In general, PDP comprises: two opposed glass substrates; a pair of electrodes systematically arranged in the glass substrates; and a gas (mainly Ne or the like) sealed therebetween. A voltage is applied across the electrodes to produce discharge within minute cells around the electrodes to emit light from each cell, thereby displaying information. Systematically arranged cells are selectively subjected to discharge luminescence in order to display information. Such PDPs are classified into two types, a direct current type PDP, wherein electrodes are exposed to a discharge space (DC type), and an alternating current type (AC type) wherein electrodes are covered with an insulating layer. Each of these types is further classified into a refresh drive system and a memory drive system according to display functions and drive systems.
FIG. 1 shows an embodiment of the construction of an AC type PDP. In the drawing, the front plate and the back plate are shown separately from each other. As shown in the drawing, two glass substrates 1, 2 are arranged parallel and opposite to each other. Both the substrates are disposed so as to be held, while leaving a given space therebetween, by means of cell barriers 3 provided, parallel to each other, on the glass substrate 2 as a back plate. Composite electrodes 6 each comprising a sustaining electrode 4 as a transparent electrode and a bus electrode 5 as a metallic electrode are provided parallel to each other on the back side of the glass substrate 1 as the front plate, and a dielectric layer 7 is provided so as to cover the composite electrode. Further, a protective layer 8 (MgO layer) is provided on the surface of the dielectric layer 7. On the other hand, address electrodes 9 are provided between the cell barriers 3 on the front side of the glass substrate 2 as the back plate so that the address electrodes 9 are parallel to each other and orthogonal to the composite electrodes 6. Further, a phosphor 10 is provided so as to cover the wall surface of the cell barriers 3 and the bottom face of cells. The AC type PDP is of a plane discharge type and constructed so that an alternating voltage is applied across the composite electrodes on the front plate and an electric field leaked in the space produces discharge. In this case, since the alternating voltage is applied, the direction of the electric field changes according to the frequency. Ultraviolet light produced by the discharge permits the phosphor 10 to emit light, and light transmitted through the front plate is viewed by an observer.
Regarding the composite electrode 6 on the front plate of the AC -type PDP, it should be noted that sole use of the sustaining electrode 4 results in high resistance value, and, hence, the bus electrode 5 is formed on the sustaining electrode 4 in order to lower the resistance value. ITO, SnO.sub.2, ZnO and the like are considered as a material for the sustaining electrode 4. In general, however, ITO is used from the viewpoints of easy film formation and patterning. On the other hand, the bus electrode is formed of a metallic material. When it is constituted by a single layer of a thin metallic film, use of a material having low resistivity, for example, Cu or Al, is considered from the viewpoint of resistance value required of the bus electrode 5. Cu, when used for the bus electrode, has poor adhesion to ITO as a layer underlying the bus electrode 5 and, in addition, as a result of firing in the formation of a dielectric layer 7 in the subsequent step, is thermally oxidized resulting in increased resistance value. On the other hand, use of Al poses a problem that the firing in the subsequent step results in thermal oxidation of the material or the roughening of the surface. Therefore, it is common practice to construct the bus electrode 5 out of a combination of dissimilar metallic materials, such as Cr/Cu/Cr or Cr/Al/Cr, rather than a single layer of a metallic thin film. In this case, Cr constituting a lower layer functions as a layer for adhesion to the underlying sustaining electrode 4, and Cr constituting an upper layer functions as a layer for antioxidation of overlying Cu or Al. The use of the above laminate structure and materials is not limited to the electrode of the above AC type PDP but applicable also to the electrode of the DC type PDP for the same reason described above in connection with the electrode of the AC type PDP. The adoption of the above laminate structure does not pose a problem associated with the single metallic layer. It, however, requires a thin film forming technique, such as sputtering or vapor deposition, and etching three times in the formation of the bus electrode, rendering the process complicated, which in turn takes a lot of time and results in unsatisfactory throughput capacity.
In view of the above, the present invention has been made, and an object of the present invention is to provide a PDP electrode which can be prepared by a simple process, and a process for producing the same.
Another object of the present invention is to provide means for forming an electrode which can realize a high display quality even in a high-definition or large-area plasma display panel.